This invention relates to electron gun assemblies for cathode ray tubes and more particularly to shielded cathode support structures for inhibiting deleterious results caused by cathode sublimation.
In cathode ray tube structures of either the so-called in-line or delta-gun construction, it is a common practice to provide insulating rods of a glass-like material. The various electrodes of the gun assemblies are embedded in the insulating rods to provide a desired spacing and electrical insulation intermediate the electrodes.
As is well known, an electrical heater is inserted into the open end of a cathode structure and a layer of electron emissive material is affixed to the opposite or closed end of the cathode sleeve. Since it is desired to utilize the heat derived from the electrical heater at a maximum efficiency in order to attain a fast warm-up of the cathode ray tube and to inhibit sublimation of the cathode structure due to the applied heat, it has been a common practice to provide a shield member and a support member for each cathode structure.
One known form of shield and support member utilized with cathodes in a cathode ray tube electron gun assembly is disclosed in U.S. Pat. No. 3,351,792 assigned to the assignee of the present application. Therein, a support member has oppositely disposed first portions formed for attachment to insulator rods and a second portion normal thereto with a central aperture. A dual-wall eyelet has one end affixed to the cathode electrode, extends upwardly along the axis of the cathode, and is bent back upon itself to provide a ledge. This entire cathode and eyelet, except for the ledge of the eyelet, pass through the aperture of the support member and the ledge and support members are attached to one another. Thus, the cathode electrode is fixedly attached by way of the eyelet to the support member.
Also, the cathode and dual-wall eyelet have upper and lower portions of different diameters to provide for attachment of the structures at the lower portions and a space therebetween at the upper portions. Moreover, the emissive material affixed to the cathode electrode extends beyond the end of the dual-walled eyelet.
As to operation, the dual-walled eyelet provides support for the cathode at the open end thereof which is furthest from the closed end having emissive material thereon whereat maximum heat is desired. Thus, support of the cathode is achieved with minimum heat loss. Also, the dual-walled eyelet is spaced from the cathode which minimizes conductive and radiated heat losses therefrom while serving as a shield for cathode sublimation.
Although the above-mentioned apparatus has been and still is extensively utilized in numerous applications, it has been found that there are circumstances wherein improvements can be made. For example, it has been found that the above-mentioned dual-wall eyelet structure tends to occupy an excessive space when employed in a cathode ray tube having a relatively small neck-size. Also, it has been found that a reduction in size of the eyelet member tends to undesirably cause increased cleaning problems when a dual-wall structure is employed.